This invention relates generally to electrophotographic duplicating apparatus and, more particularly, is directed to the use of curvilinearly shaped foraminated image storing devices capable of having stored thereon charge patterns corresponding to light and dark areas of a graphic original. Such devices are known in this field as modulators. They are capable of selectively transmitting and otherwise blocking the passage therethrough of charged particles directed towards its surface in conformance to the charge pattern established thereon.
The term charge pattern will be referred to herein as the charge distribution system created on the modulator. The charge retaining portions will produce fields capable of either blocking the transmission of ions directed to the modulator or permitting them to be transmitted. For the purpose of the description of the invention which follows, the term charged particles will be deemed to define not only toner particles but also gas ions. The term block when used herein will describe the condition of the charged particle not passing through the aperture in the modulator due to its being attracted to the modulator or otherwise repelled from its surface and being returned into the stream of particles to again be projected elsewhere against the modulator. Charged particles which are referred to as being transmitted means that the field established across the aperture propels the particle through, or absent a field the charged particle will move through the aperture as part of its normal movement.
Various forms of modulators are known in this art. Some are constructed of two layers, others with three layers comprising a conductive layer, an intermediate layer of photoconductor material covered with a third insulating layer and still others with four layers. Depending on the arrangement of layers comprising the modulators, they will require different processing steps in order to provide a charge distribution system thereon, but in the final result, all modulators are capable of selectively transmitting or passing charged particles.
In certain of the two-layered constructions, it is necessary to maintain the pattern of light and shadow simultaneous with the projection of the gas ions, such as described in Snelling U.S. Pat. No. 3,220,324, since such a screen does not have a memory.
In the three-layer constructions, the modulator is capable of retaining the charge pattern on the insulating surface for extremely long periods of time and therefore produces a charge distribution system thereon which is capable of surviving independently of any simultaneous projection of the light pattern.
The operation and construction of the curvilinear electrodes of this invention will be described in the environment of a duplicating apparatus which utilizes a modulator having a charge distribution system defined herein, namely, a three-layer photoconductive screen having a substantially long memory. It will be understood, however, that the advantages and technical advancement in ion optics to be realized from practicing this invention can be realized to equal advantage with any type of foraminated structure capable of selectively blocking or transmitting charged particles therethrough to be collected on a dielectric receiving medium supported on a collecting electrode.
A detailed description of the operation and construction of the modulators referred to hereiin will be found in U.S. Pat. application Ser. No. 423,883, filed in the name of John D. Blades, et al, and assigned to the same assignee as the instant invention. The steps necessary to impart a charge distribution to the surface of such a modulator require the application of a blanket electrostatic charge to the insulating layer which results in the injection of oppositely poled charges into the conductive screen layer in the direction of the insulating layer. The injection of such oppositely poled charges, which ultimately are bound at the interface between the photoconductive layer and the insultating layer, occurs by virtue of the rectifying properties of the photoconductive layer. This dipole charge state could also be achieved by applying a blanket charge simultaneous with flood illumination using a non-rectifying photoconductor. The insulating layer will thereby have a uniform field applied across its thickness erasing any previous charges thereon.
As the next step, the modulator is given a simultaneous exposure to a corona electrode connected to an AC supply and pattern of light and shadow. The AC corona serves to erase the charges on the insulating layer. The charges which are bound at the interface are leaked to ground by virtue of the photoconductive layer being rendered conductive in response to exposure to electromagnetic radiation.
In the insulating areas corresponding to the dark portions of the pattern of light and shadow, the AC corona has the effect of connecting the insulating layer to the conductive layer causing some of the charges to be transferred to the metal base thereby causing oppositely poled charges to be bound at the interface between the photoconductive layer and the metallic layer. In the dark areas, therefore, the outer insulating layer and the conductive layer are at an equal potential level. The net charge across all three layers is zero, and the ability of the modulator to selectively block or transmit charged particles cannot occur until the entire surface is flood illuminated.
As a final step, the modulator is given a flood exposure of electromagnetic radiation which now causes the intermediate photoconductive layer to become conductive, including the previously unexposed portions causing any trapped charges to leak off to ground. This leaves only those charges that are bound at the interface between the photoconductive layer and the insulating layer by virtue of the charges present on the surface of the insulating layer. Hence, a dipole charge system is created across the insulating layer and those areas corresponding to the shadow or dark portions of the graphic original.
Having described the creation of a charge distribution system on the modulator, its utilization in a reproduction system requires that charged particles be projected onto the conductive surface of the modulator and provision made for the collection of those charged particles which are transmitted through the modulator onto a dielectric paper in an image-wise pattern and then developed according to conventional procedures.
Heretofore, the projection of such charged particles through modulators which were planar in their configuration could be arranged so that any collection electrode was in a plane parallel to the modulator. This arrangement obviated any problem of image distortion.
The instant invention deals with the construction and arrangement of the various electrodes necessary to achieve the movement, collection propagation of the gas ions transmitted through a curved modulator onto a collection electrode without any image distortion thereby achieving the same results that can be achieved by the electrode and the modulator when disposed in parallel planes with respect to one another.